1. Field of the Invention
The invention relates, in general, to surgical instruments and, more particularly, to surgical instruments for use in the repair of bone fractures.
2. Description of Related Art
In the treatment of certain bone fractures, such as many fractures of the fibula, it is often necessary to distract or separate two bone fragments longitudinally. In such injuries, the two fragments often shorten and override one another. In order to restore alignment, a surgeon must restore length by pulling the fragments apart, back to their normal position. Distraction is also often required for other long bone fractures as well, as the pull of the associated muscles can cause long bone fractures to shorten.
One common method of addressing this shortening of long bone fractures is to manually grasp a distal end of an appendage and manually pull on it longitudinally and away from the proximal end, in order to regain the proper length relationship of the two fragments. However, this can be difficult to perform, as it this requires the surgeon to pull directly against the associated muscles. Moreover, manually pulling on a distal end of a limb does not necessarily produce the required force to distract a fractured bone. In particular, the presence of additional, unfractured bones in the forearm or lower leg will tend to resist any longitudinal pull on the hand or foot, respectively, inhibiting such manual distraction of the fracture. Furthermore, this approach commonly requires two persons to participate: one is required to manually distract the bone fragments, while another applies and tightens the fixation to the fracture.
Another method of distracting is to apply a first bone clamp to a distal portion of the bone above the fracture, apply a second bone clamp to a proximal portion of the bone below the fracture, and then pull the two bone clamps apart. However, a bone clamp may potentially slide on the bone if it is not clamped hard enough. Moreover, if the bone clamp is clamped too hard, it risks crushing or otherwise further damaging the fragment. Also, it is often difficult to generate sufficient clamping force, as the bone clamps are usually not rigidly attached to the respective fragments. Clamping the fragments has two additional disadvantages. Firstly, it requires further soft tissue dissection to expose each bone fragment sufficiently to enable a clamp to be placed around the fragment. Secondly, it may be difficult to apply a plate to the surface of the bone, as the presence of the bone clamps may provide insufficient remaining space in which to position the plate. In other words, a surgeon may use bone clamps to distract the bone fragments to the necessary length, only to discover that a bone plate cannot be readily applied for fixation, as the clamps would first need to be removed, resulting in a loosening of the reduction.
Another method of pulling apart the bone fragments is to first insert a transverse pin into the distal fragment. The distal fragment is then distracted by pulling on the pin. However, this has the undesired effect of creating yet another, temporary hole in the fragment. Moreover, the insertion of any pin can result in inadvertent damage to surrounding nerves or vessels as it is placed across the bone, as it usually requires placement through surrounding soft tissue. Moreover, additional soft tissue exposure can further devascularize the bone and can thus impair healing.
When treating certain bone fractures, situations also arise where it is desirous to create compression, rather than expansion, between two bone fragments adjacent a fracture. For example, a surgeon applying a bone plate may wish to create compression between two bone fragments in order to stimulate healing, as bone fractures typically heal better in compression, in comparison to the absence of compression.
Several techniques have been used for creating compression between bone fragments when a plate is applied. In one technique, a surgeon places a bone screw beyond the end of the plate and applies an outrigger apparatus that couples to the last hole in the plate. Upon turning a screw in the outrigger apparatus, the apparatus pulls the end of the plate towards the screw placed beyond the plate. The surgeon then finishes fixation of the plate, removes the outrigger, and finally removes the outrigger anchoring screw beyond the plate. This technique has the disadvantage of requiring significant additional soft tissue dissection to expose bone proximate the fracture, to enable placement the bone screw and application of the outrigger apparatus beyond the end of the plate. There is also additional required time during surgery to expose the additional bone, to fix the additional bone screw, to apply the outrigger apparatus, and subsequently to remove the outrigger apparatus and additional bone screw.
Another technique for gaining compression is the dynamic compression plate technique. In this technique, a hole in a fixation plate is specially designed to include a countersink portion, to allow a screw head to be seated within the plate, and to further include a squared off profile in cross section at one edge. The head of the bone screw has a rounded cross section. The screw is initially placed up against the end of the hole. As the rounded head of the screw comes down into the hole as the screw is threaded into the underlying bone, it hits the plate, forcing the plate to move sideways to allow the screw head to seat inside the countersink portion of the hole. The dynamic compression plate technique typically requires the fixation plate to have a significant minimum thickness in order to work properly, as the screw head has to sit within the plate. This requirement for a relatively bulky plate can result in irritation of overlying soft tissues, and can result in stress shielding of the bone underneath the relatively thick, stiff plate, potentially resulting in loss of bone mass and osteoporosis. Moreover, the amount of compression displacement achieved from the dynamic compression plate technique is limited by the size of the associated screw head.